Stena Impero, a UK-flagged vessel owned by Stena Bulk, is seen at Bandar Abbas port, in this undated handout photo. The UK has called Iran's capture of the Stena Impero in the Strait of Hormuz on Friday a 'hostile act' and says it's not ruling out responding with sanctions.
Image: Tasnim News Agency/Handout via REUTERS

Iran's ambassador to Britain warned against escalating tensions on Sunday as a UK official declined to rule out sanctions in response to Tehran's seizure of a British-flagged oil tanker.

Britain has called Iran's capture of the Stena Impero in the Strait of Hormuz on Friday a "hostile act".

Britain needs to contain "those domestic political forces who want to escalate existing tension between Iran and the UK well beyond the issue of ships," Iran's envoy to Britain Hamid Baeidinejad said on Twitter.

"This is quite dangerous and unwise at a sensitive time in the region," he said, adding that Iran "is firm and ready for different scenarios."

Britain's junior defence minister Tobias Ellwood did not rule out the possibility of targeting Tehran with sanctions in response.

"Our first and most important responsibility is to make sure that we get a solution to the issue to do with the current ship, make sure other British-flagged ships are safe to operate in these waters and then look at the wider picture," Ellwood told Sky News.

Asked about the possibility of sanctions, he said: "We are going to be looking at a series of options ...We will be speaking with our colleagues, our international allies, to see what can actually be done."

Tehran's seizure of the Stena Impero followed the July 4 capture by Royal Marines of the Grace 1 tanker carrying Iranian oil near Gibraltar.

British foreign minister Jeremy Hunt on Saturday said Tehran's actions showed "worrying signs Iran may be choosing a dangerous path of illegal and destabilising behaviour after Gibraltar’s legal detention of oil bound for Syria."

All crew safe

In a letter to the UN Security Council, Britain said the Stena Impero was approached by Iranian forces in Omani territorial waters where it was exercising its lawful right of passage, and that the action "constitutes illegal interference."

British warship HMS Montrose radioed an Iranian patrol vessel to warn it against boarding the Stena Impero, according to radio messages provided to Reuters by maritime security firm Dryad Global.

Iran said the seized tanker "risked maritime safety" in the Strait of Hormuz, through which almost a fifth of the world's annual oil consumption passes.

"We are required by regulations to investigate the issue ... the duration of the investigation depends on the level of co-operation by the involved parties," Allahmorad Afifipour, head of Iran's Ports and Maritime Organisation in Hormozgan Province, told state TV.

He added that all 23 crew members aboard the ship are "safe and in good health in Bandar Abbas port".

The vessel's Sweden-based owner, Stena Bulk, said it hoped to visit the crew, who are from India, Latvia, the Philippines and Russia. India has called on Iran to release the ship's 18 Indian crew members.

Tehran for weeks has vowed to retaliate for the seizure of the Grace 1 tanker by British forces.

"The Revolutionary Guards responded to Britain's hijacking of the Iranian tanker," parliament speaker Ali Larijani told a parliament session aired live on state radio.

Waivers

Iran is feeling the pressure of US sanctions imposed on its banks and oil exports by US President Donald Trump last year after he pulled the US out of a 2015 international pact with Iran designed to curb Tehran's nuclear program.

"The export of oil is one of the issues in which we have limitations and the US and its allies have caused restrictions for us and we have to be sensitive," Iran's oil minister Bijan Zanganeh said, state media reported on Sunday.

He said the country's oil exports had not been impacted so far by the recent tanker incidents in the Gulf.

Iran has repeatedly threatened to close the Strait of Hormuz if it cannot export its oil because of the sanctions but cannot legally do so as part of the waterway is in Oman’s territorial waters.

Ships using the Strait also pass through Iranian waters, which are patrolled by Iran’s Revolutionary Guards Navy.

Oman has urged Iran to release the tanker and called on all parties to exercise restraint and resolve differences diplomatically, state broadcaster Oman TV News reported.

"Iran is displaying its power without entering a military confrontation. This is the result of America's mounting pressure on Iran," said an Iranian official, who asked not to be identified.